JP5355659B2 - Interferometry apparatus and measurement origin determination method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an interference measuring apparatus capable of highly accurately setting an origin after measurement and capable of highly accurately measuring the displacement information (absolute displacement information) of an object to be measured. <P>SOLUTION: The interference measuring apparatus includes: first multiplexing means for multiplexing a first beam from first light source means and a second beam from second light source means; an optical system for dividing the beam obtained by multiplexing the first beam and the second beam into two beams, making one beam incident on a measuring surface of the object to be measured, making the other beam incident on a reference surface, and multiplexing a reflected beam from the measurement surface and a reflected beam from the reference surface; light receiving means for receiving a beam formed by two divided first beams included in the reflected beams from the measurement surface and the reference surface and a beam formed by two second beams; and determination means for determining a measurement origin by using a first signal based on the first beams received by the light receiving means and a second signal based on the second beams received by the light receiving means. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to an interference measuring apparatus and a measurement origin determining method for detecting position variation information of an object without contact, and in particular, when detecting displacement information, an origin position as an origin is added to detect absolute position transition information. It is suitable when doing.

  Laser interference measuring devices such as Michelson interferometers using laser light are widely used as devices that measure length with nanometer-level accuracy and resolution.

  In the laser interference measurement device, the interference wave generated by the displacement of the object to be measured is a sine wave, and the amount of displacement can be obtained with nanometer level accuracy and resolution by accumulating the wave numbers and reading the phase of the sine wave. .

  Various devices for obtaining displacement information (positional information) of a surface to be measured using an interference signal obtained by a Michelson interferometer have been proposed (Patent Document 1).

  In the displacement detection apparatus of Patent Document 1, displacement information of a surface to be measured provided on a magnetic head arm is detected using optical interference.

  Specifically, a probe indicating arm for positioning is provided coaxially with the rotation axis of the magnetic head arm.

  An optical position detection sensor unit for detecting whether or not the end face position (surface to be measured) of the magnetic head arm is at an appropriate position is attached to the probe instruction arm.

  This optical position detection sensor unit is provided with a detection system including a quarter-wave plate, a phase diffraction grating, a light receiving element, and the like for positioning the side surface of the magnetic head arm using an interference signal.

  In addition, a focus detection optical system including a deflection plate, a condensing lens, a four-divided sensor, and the like is provided in order to detect positional information of the measurement target surface in the optical axis direction.

JP 2001-76325 A

  As for laser interference by the interference measuring device, an output signal is obtained as a sine wave. For this reason, it is possible to measure nanometer-order resolution from the wave number and phase, but it is impossible to measure the absolute position only by displacement. As a method for obtaining the absolute displacement information of the measured object, it is necessary to provide a reference point (origin) and obtain the relative position therefrom.

  In this case, in order to obtain an accurate absolute position, a reference point (origin) having an accuracy equal to or less than the wavelength of the output sine wave of laser interference (in the above example, 0.2 μm) is required.

  In the focus detection optical system of the displacement detection apparatus of Patent Document 1, the origin of the surface to be measured is obtained by detecting the ratio of the amount of light incident on each sensor of the four-divided sensor and does not use an interference signal.

  For this reason, it is difficult to detect the position information of the surface to be measured with the accuracy of the wavelength order.

The present invention has an object to provide an interference measuring apparatus and the origin determination method capable of setting an origin with high accuracy.

Interference measuring apparatus of the present invention, the first light source means and said first second light source means for emitting a second light beam having low coherence than the light beam that emits first light flux coherent When the a first multiplexing means for first multiplexing said optical beam second beam, said first beam and said second light beam and the light beam is combined, the first a portion of a part and the second light flux of the light beam is divided into two beams, each including the division by applying light beams of one resulting et a the measuring surface, the other obtained by the division A light beam is incident on a reference surface, the reflected light beam from the measurement surface and the reflected light beam from the reference surface are combined , and the reflected light beam from the measurement surface and the reflected light beam from the reference surface are combined. Reflected from the measurement surface on which the two light beams included in the first and second light beams included in the first and second light beams are combined. The receiving light beams formed by the interference of the reflected light beam and to an optical system for interfering two of said second light beam contained respectively, said two first light beam from the reference surface and 1 Based on the first signal and the second signal, and a light receiving means for receiving the light beam formed by the interference of the two second light beams and outputting the second signal, Determining means for determining a measurement origin.

Measurement origin determination method of the present invention, the measurement a starting point determination method, if a second beam having low coherence than the first light flux and the first light flux of coherent for interference measurements a step you wave the first light flux which the light flux and the second light beams are combined, a portion of two each containing part and the second light flux of the first light flux divided into light beams, one of the light beams obtained by the division to be incident on the measurement surface, said other light beam obtained by the division is incident on the reference surface, and the reflected light beam from the measuring surface from the reference surface the reflected light flux multiplexes, by interfering two of the first light beam that is included in each of the reflected light beam from the reference surface and the reflected light beam from said measurement plane made the multiplexing, the multiplexing Included in the reflected light beam from the measurement surface and the reflected light beam from the reference surface, respectively. A step of interfering two of said second light beam is, the light beams formed by the interference of two of the first light flux and outputs a first signal by receiving said two of said second beam wherein the steps receiving light flux you output a second signal formed by interference, determining a measurement origin based on the first signal and the second signal, to have a It is said.

According to the present invention, it is possible to obtain an interference measurement apparatus and a measurement origin determination method that can set the origin with high accuracy.

Schematic of optical arrangement of Example 1 Explanatory drawing of the power spectrum of optical LD and optical SLD of Example 1 Explanatory drawing of visibility of optical SLD of Example 1 Waveform diagram of UVW interference signal output of Example 1 Waveform diagram of A phase and B phase calculated from interference signal UVW output of Example 1 Waveform diagram of U interference signal output and O interference signal output of Example 1 Schematic of optical arrangement of Example 2 Explanatory drawing of the power spectrum of optical LD and optical SLD of Example 2 Waveform diagram of U interference signal output and (U + O) interference signal output of Example 3

  The interference measuring apparatus according to the present invention includes a first light source unit that emits a coherent first light beam, and a second light source unit that emits a second light beam having a coherence lower than that of the first light source unit. And first combining means for combining the first light flux and the second light flux. The light beam obtained by combining the first light beam and the second light beam is divided into two light beams each including at least a part of the first light beam and the second light beam.

  An optical system that causes one of the divided light beams to enter the measurement surface of the object to be measured, the other light beam to enter the reference surface, and combines the reflected light beam from the measurement surface and the reflected light beam from the reference surface; Have Light receiving means for receiving the light beam formed by the two divided first light beams included in the reflected light beam from the measurement surface and the reflected light beam from the reference surface via the optical system. Further, the light receiving means receives a light beam formed by the two divided second light beams included in the reflected light beam from the measurement surface and the reflected light beam from the reference surface.

  Determining means for determining a measurement origin based on the output of the light receiving means. The determining means determines the measurement origin using a first signal based on the first light beam received by the light receiving means and a second signal based on the second light beam received by the light receiving means. .

  At this time, the optical system divides the light beam obtained by combining the first light beam and the second light beam into two light beams each including at least a part of the first light beam and the second light beam. Including splitting surfaces. The second signal is a signal that is output when the optical path length from the divided surface to the measurement surface is equal to or substantially equal to the optical path length from the divided surface to the reference surface.

  At this time, the determination unit includes a detection unit that detects a peak of the second signal, and the relationship between the output of the detection unit and the first signal that is a periodic signal is a predetermined relationship. Determine the measurement origin.

  Further, the measurement origin determining method of the present invention combines the coherent first light beam from the first light source and the second light beam having a lower coherence than the first light beam from the second light source. And a multiplexing step. The light beam obtained by combining the first light beam and the second light beam is divided into two light beams each including at least a part of the first light beam and the second light beam. Then, the split one light beam is incident on the measurement surface of the object to be measured, the other light beam is incident on the reference surface, and the reflected light beam from the measurement surface and the reflected light beam from the reference surface are combined. Has a ratio wave step.

  A light receiving step of receiving a light beam formed by the two divided first light beams included in the reflected light beam from the measurement surface and the reflected light beam from the reference surface; Further, in the light receiving step, a light beam formed by the two divided second light beams included in the reflected light beam from the measurement surface and the reflected light beam from the reference surface is received by a light receiving unit. Determining the measurement origin using a first signal based on the first light beam received by the light receiving means and a second signal based on the second light beam received by the light receiving means.

  In the embodiment of the present invention, low-coherence light having a spectral half-width of about 30 nm is multiplexed on the same optical system as that of a high-coherence laser beam such as a single mode semiconductor laser. The origin (measurement origin) is determined from the interference output peak (amplitude peak) of the low coherence light and the interference output of the high coherence laser light.

  That is, when the spectral width of low coherence light is large, the interference output waveform of the low coherence light is such that the measured surface of the high coherence laser light is near the reference optical path and the reference point near the optical path. The waveform is substantially the same as the waveform of the interference output.

  The maximum is obtained when the distance between the reference surface and the surface to be measured is equal. Thereby, the origin synchronized with the interference output of the high coherence laser beam is determined.

[Example 1]
1A and 1B are a main part side view and a main part front view of Example 1 of the present invention.

  In the first embodiment, the origin detecting means is applied to a small interference measuring apparatus.

  A single-mode semiconductor laser LD (hereinafter referred to as “semiconductor laser LD”) (first light source means) uses a DFB (Distributed Feedback) laser having a stable oscillation laser wavelength of 0.78 μm.

  The linearly polarized divergent light and light LD (first light beam) emitted from the semiconductor laser LD are converted into parallel light by the collimator lens COL1.

  On the other hand, a super luminescent diode SLD (hereinafter referred to as a “diode SLD”) having a center wavelength of about 30 nm and a center wavelength of about 0.84 μm, which has a different center wavelength from that of the light LD and has low coherence (second light source means) Is used.

  Light SLD (second light flux) from the diode SLD is converted into parallel light by the collimator lens COL2. The light LD from the collimator lens COL1 and the light SLD from the COL2 are combined on the same optical axis (the principal rays of both light beams coincide) by the dichroic mirror (combining means) DM1. The lens LNS1 condenses and illuminates the focal plane position P1 of the lens LNS2 via the half mirror NBS.

  The light beam from the position P1 is emitted from the lens LNS2 as a parallel light beam whose optical axis is slightly oblique. Then, it is separated into two light beams by the polarization component by the polarization beam splitter (light splitting means) PBS1. Reflected light (S-polarized light) from the polarization beam splitter PBS1 is incident on a reference mirror (reference surface) M1, and transmitted light (P-polarized light) from the polarization beam splitter PBS1 is a measurement mirror (measurement surface) M2 as a measurement target surface. It is made incident on.

  Then, the respective reflected lights are combined via the polarization beam splitter PBS1, and the focal plane position P2 of the lens LNS2 is condensed and illuminated, and returned to the original optical path by the reflection film MO provided in the vicinity thereof. .

  The reflected light from the position P2 is emitted as a parallel light beam from the lens LNS2, separated into two light beams by the polarization beam splitter PBS1, and the reference mirror M1 is illuminated with the reflected light (S-polarized light). At this time, the optical paths of the light beams that are split by the light splitting means PBS1 of the first light beam LD and the second light beam SLD, enter the reference surface M1, and are reflected by the reference surface M1 are common.

  Further, the measured mirror (measured surface) M2 is illuminated with transmitted light (P-polarized light).

  The respective reflected lights are combined through the polarization beam splitter PBS1 to collect and illuminate the focal plane position P1 of the lens LNS2, and the light flux is extracted from there to the light source side. (S-polarized light makes two reciprocations between the reference surface M1 and the beam splitter PBS1, and P-polarized light makes two reciprocations between the measured surface M2 and the beam splitter PBS1). These light beams are extracted to the light receiving system side by a non-polarizing beam splitter (half mirror) NBS, transmitted through the quarter-wave plate QWP, and converted into linearly polarized light whose polarization azimuth rotates in accordance with a change in phase difference.

Thereafter, in order to separate the light LD and the light SLD, the light LD, which is the first light flux, is transmitted through the dichroic mirror DM2 having the same configuration as the dichroic mirror DM1 through the condenser lens CON and the aperture AP, and the second light flux Reflects and separates the light SLD.

  The light LD is detected by a light receiving system LD (first light receiving means). That is, the light is split into three light beams by the beam splitting element GBS, and the respective light beams are incident on the respective light receiving portions of the three-split light receiving element PDA via the polarizing element array 3CH-POL arranged by shifting the polarization axes by 60 °. Yes. As a result, three interference signals UVW whose phases are shifted from each other by 120 degrees based on the out-of-plane displacement of the measurement target surface (mirror) M2 are detected. From this interference signal UVW, the A phase and B phase whose phases are shifted by 90 ° by the calculation means SPC are set to A = 2/3 × {U− (V + W) / 2}, B = 1 / √3 × (V−W). It is obtained by the calculation of

  On the other hand, the light SLD reflected by the dichroic mirror DM2 is detected by a light receiving system SLD (second light receiving means). That is, the light enters the light receiving element PD2 via the polarizing element POL2, and outputs the interference signal O when the surface to be measured is near the optical path with the reference surface.

  Here, the polarization direction of the polarization element 3CH-POL-1 of the polarization element array 3CH-POL corresponding to the U output and the polarization direction of the polarization element POL2 with respect to the light SLD becomes a peak when the optical path difference between the measured surface and the reference surface is zero. Is arranged. As a result, the U waveform and the A phase become cosine waveforms having the origin at the zero optical path difference between the measured surface M2 and the reference surface M1.

  Further, the O output can be output in the form of a cosine wave in which the measured surface M2 has a zero optical path difference between the measured surface M2 and the reference surface M1, and attenuates as the distance from the origin is increased.

  The members in the optical path from the measured surface M2 and the reference surface M1 to the light receiving elements PD2 and PDA form one element of the interference part.

  FIG. 2 shows power spectra of the light LD from the semiconductor laser LD and the light SLD from the diode SLD.

  The power spectrum of the light LD from the semiconductor laser LD is an emission line of 0.78 μm. The power spectrum of the light SLD from the diode SLD is approximated to a Lorentz type power spectrum having a center wavelength of 0.84 μm and a half width of 30 nm. The power spectrum S (Δλ) with respect to the wavelength shift Δλ from the center wavelength (0.84 μm) of the optical SLD is given by the following equation.

S (Δλ) = (ΔΛ / 2) ² 2 / {Δλ ² + (ΔΛ / 2) ² } (1)
: ΔΛ indicates a half width, which is 30 nm here.

  The dichroic mirrors DM1 and DM2 shown in FIGS. 2 to 1 have a boundary between transmission and reflection characteristics in the vicinity of a wavelength of 0.8 μm. The dichroic mirror DM1 can multiplex the light flux and the dichroic mirror DM2 can demultiplex the light flux.

  Now, the interference signal UVW from the semiconductor laser LD has a sufficiently long coherence. On the other hand, the coherence and visibility V (ΔVl) of the interference signal O by the diode SLD can be approximated by the following equation from the inverse Fourier transform of one equation.

V (ΔVl) = EXP {−πΔΛ / λ ² } ΔVl (Expression 2)
: Λ is the center wavelength of the optical SLD, here 0.84 μm
: ΔVl is optical path length difference FIG. 3 is a diagram showing the relationship between the optical path length difference Δ1 and the visibility V at this time.

  On the other hand, an interference signal UVW obtained by the semiconductor laser LD obtained by the light receiving element PDA is shown in FIG. FIG. 5 shows the interference signals A and B, which are generated from the interference signal UVW and are 90 ° out of phase. FIG. 6 shows an interference signal O obtained by the diode SLD in the vicinity of the equal optical path obtained by the light receiving element PD2 and an interference signal U obtained by the semiconductor laser LD. The horizontal axis indicates the optical path difference between the surface to be measured and the reference surface SLD. Since the light reciprocates twice, the displacement of the surface to be measured is 1/4. From the figure, the interference signal O due to the diode SLD is substantially the same cosine curve as the interference signal U due to the semiconductor laser LD at the equal optical path (optical path difference O), and the peak can be determined to be larger than the adjacent peak.

  Therefore, by detecting the peak (intensity) of the interference signal O from the diode SLD, the origin synchronized with the interference signal U from the semiconductor laser LD is determined with high accuracy.

  Note that the origin may be determined from the relationship between the preset value and the interference signal B, instead of the peak value of the interference signal O.

  The interference signals A and B, which are generated from the interference signal UVW by the semiconductor laser LD and are 90 ° out of phase, are based on interference measurement using two reciprocating optical paths. For this reason, it is a sinusoidal signal having a period of 1/4 of the wavelength of the interference signal U source by the semiconductor laser LD.

When a semiconductor laser LD with a wavelength of 0.78 μm is used, a sine wave signal with a period of 0.195 μm is obtained. By counting the wave number and calculating the phase by tan ^-1 (B / A), it is possible to detect the relative displacement with nanometer order resolution.

  Further, by resetting the wave number counting at the peak of the interference signal O generated by the diode SLD, the absolute value can be measured with a resolution of nanometer order at the origin.

As described above, in the first embodiment, the interference signal formed by the light LDs and the interference signal formed by the light SLDs in the interference unit are detected by the light receiving element PDA and the light receiving element PD2 as light receiving means.

  Then, from the interference signal obtained by the light receiving means, the position of the equal optical path from the light splitting means PBS1 of the measurement reflecting surface M and the reference surface M1 is measured as the measurement origin of the displacement information to obtain the absolute displacement information.

  Specifically, from the intensity information of the interference signal provided by the light receiving means PD2, the position of the equal optical path of the light splitting means PBS1 on the measurement reflecting surface M2 and the reference surface M1 is set by the period of the interference signal obtained by the light receiving means PDA. ing. Then, absolute displacement information is obtained as a measurement origin of the displacement information.

[Example 2]
FIG. 7 is a schematic view of the essential portions of Embodiment 2 of the present invention. The second embodiment differs from the first embodiment in the following points.
(A) The driving of the semiconductor laser LD and the diode SLD is alternately turned on and off when the origin is detected.
(B) The SLD light receiving system also serves as the polarizing element array 3CH-POL and the three-divided light receiving element PDA in the light receiving system LD for interference signals from the semiconductor laser LD. The interference signal O of the optical SLD uses a signal from PDA-1 corresponding to the interference signal U of the three-divided light receiving element PDA (PDA1 to PDA3).

According to each lighting, the interference signal UVW by the light LD and the interference signal O by the light SLD are sampled and separated by the signal processing SPC, and interpolation estimation is performed while each interference signal is OFF, and the interference signal UVW and light by the continuous light LD An SLD interference signal O is obtained.
(C) No separation by wavelength is required. As shown in the power spectrum of the light LD and the light SLD shown in FIG. 8, by reducing the wavelength difference between the light LD and the light SLD, the characteristic deviation due to the wavelength of the polarization beam splitter PBS or the like can be reduced. A half mirror is used as the multiplexing means HM.

  From the interference signal O of the optical SLD and the interference signal UVW of the optical LD thus obtained, the origin is determined in synchronism with the interference signal from the optical LD as in the first embodiment.

  In the second embodiment, when the origin is detected, the light SLD is turned on and off and sampling is performed in time series. Therefore, the movement of the measurement target surface M2 needs to be sufficiently slower than the sampling frequency.

  In general, the surface to be measured M2 is generally slower than electrical sampling as long as it is mechanically moved, and the origin detection is easy.

[Example 3]
The configuration of the third embodiment of the present invention is substantially the same as FIG.

  In the third embodiment, the semiconductor laser LD is always lit instead of turning on and off alternately when the origin of the semiconductor laser LD and the diode SLD is detected in the second embodiment. Then, the driving of the diode SLD is adjusted to ON / OFF.

  Specifically, the interference signal UVW from the semiconductor laser LD is used when the diode SLD is OFF.

  When ON, a signal in which the interference signal UVW from the semiconductor laser LD and the interference signal O from the diode SLD are superimposed is sampled and separated by the signal processing SPC. Each interference signal is estimated and interpolated to obtain a continuous interference signal UVW and a signal in which the interference signal O is superimposed on the interference signal UVW.

  In FIG. 9, the interference U is superimposed on the interference signal UVW and the waveform of the signal U of the continuous interference signal UVW estimated and interpolated in the vicinity of the equal optical path from the light splitting means PBS on the measurement surface M2 and the reference surface M1. The waveform of the signal (U + O) of the signal is shown.

  From the signal (U + O) obtained by superimposing the interference signal U from the optical LD on the interference signal O from the optical SLD and the interference signal UVW from the optical LD obtained in this way, the origin is synchronized with the interference signal V from the optical LD as in the first embodiment. It has established.

  In the third embodiment, the semiconductor laser LD is always lit, but conversely, the diode SLD may be lit constantly to drive the semiconductor laser LD on and off.

  The semiconductor laser LD is preferably maintained at a constant temperature in order to stabilize laser oscillation.

  However, when ON-OFF, due to the thermal resistance of the semiconductor laser element, the temperature change of the light emitting portion of the semiconductor laser element occurs at the time of ON, and there is a possibility that the laser single mode oscillation becomes unstable. For this reason, it is preferable to always turn on the semiconductor laser LD as in the third embodiment.

  As described above, in the third embodiment, the driving of only one of the two light source means is turned on and off. The interference light based on the light flux from the other light source means is detected in accordance with the extinction of one of the light source means. The light receiving means receives an interference waveform in which the interference light of the light SLD is superimposed on the interference light of the light LD in accordance with the lighting of one of the light source means. Then, the interference signal waveform based on the light flux from one light source means turned on or off or the interference signal waveform based on the light flux from the other light source means is estimated and interpolated. Thereby, the position of the equal optical path from the light splitting means on the measurement reflecting surface and the reference surface is set as the measurement origin.

  In each of the embodiments described above, a super luminescent diode SLD is used as a light source of low coherence light, and the power spectrum is approximated to a Lorentz type. However, in this case, the visibility and the envelope of the interference signal O are also different. It ’s different.

  However, as the half-value width of the power spectrum is larger, the peak at the origin is easier to detect than the adjacent peak, and detection is difficult when the half-value width of the spectrum is small. The power spectrum needs to be able to detect the peak (amplitude peak) of the interference signal of the low coherent light when the reference surface and the surface to be measured have equal optical path lengths.

  As a small light source of low coherent light, the directivity is wide and the light use efficiency is low, but a current confinement type point light source light emitting diode is also useful.

  It can also be applied to a gas laser interferometer that uses a corner cube as an object to be measured. A white point light source composed of a xenon lamp light source and a pinhole is also useful as a light source of low coherent light.

  In addition to the DFB laser diode, a single mode surface emitting semiconductor laser (VCSEL) controlled at a constant temperature, a gas laser such as He-Ne, or the like can be used as a stable high coherence light source.

  As described above, according to each embodiment, the origin of nanometer-order resolution can be obtained in synchronization with the output sine wave of laser interference.

  Therefore, it becomes easy to measure absolute position information with a resolution of nanometer order.

LD Single mode laser light source SLD Super luminescent diode COL1, COL2, COL3 Collimator lens LNS1, LNS2 Lens DM1, DM2 Dichroic mirror HM Half mirror PBS Polarizing beam splitter NBS Non-polarizing beam splitter GRN Refractive index distribution type rod-shaped lens 3CH-POL POL2 Polarizing element PDA Light receiving element array PD Light receiving element M1 Reflective surface to be measured M2 Reference reflective surface P1, P2, P3 Condensing position f Focal length GBS Beam splitting element

Claims (15)

First light source means for emitting a coherent first light beam;
A second light source means for radiating a second light beam having low coherence than the first light flux,
First combining means for combining the first light flux and the second light flux;
Wherein the first light flux which the light flux and the second light beams are combined, and divided into a portion of a part and the second light flux of the first light beam into two light beams each containing the one of the light beam resulting et a by division is incident on the measurement surface, said other light beam obtained by the division is incident on the reference surface, if a reflected light beam from the reference surface and the reflected light beam from the measuring surface And the two reflected first light beams included in the reflected light beam from the measurement surface and the reflected light beam from the reference surface are made to interfere with each other, and the measurement is performed. An optical system for interfering the two second light beams respectively included in the reflected light beam from the surface and the reflected light beam from the reference surface ;
A light beam formed by the interference of the two first light beams is received and a first signal is output , and a light beam formed by the interference of the two second light beams is received and a second signal is received. Light receiving means for outputting
Interference measuring apparatus characterized by having a determining means for determining a measurement origin on the basis of said second signal and said first signal. The interference measuring apparatus according to claim 1, wherein the determining unit determines the measurement origin based on a relationship between a peak of the second signal and the first signal . The interference measurement according to claim 1 , wherein the determination unit determines the measurement origin based on a relationship between a preset value of the second signal and the first signal. apparatus. The optical system includes a dividing surface forming the split,
The second signal according to claim 1, characterized in that it comprises an optical path length from the divided face to the measuring surface, a maximum value when the optical path length are equal from the splitting surface to the reference plane The interference measuring apparatus according to any one of claims 3 to 3 . 5. The interference measuring apparatus according to claim 1, wherein the first light source unit and the second light source unit are driven alternately. The interference measurement apparatus according to claim 5, wherein the first signal and the second signal are interpolated. While one of the first light source means and the second light source means is being driven, the other of the first light source means and the second light source means is driven and stopped. Done
  The light receiving means is formed as one of the first signal and the second signal by a light beam formed by interference of the two first light beams and by interference of the two second light beams. A light beam formed by interference between the two first light fluxes as the other of the first signal and the second signal. And outputting a signal obtained by receiving one of the light beams formed by the interference of the two second light beams. Interference measurement device. Based on a signal obtained by receiving both and a signal obtained by receiving the one, a light beam formed by interference of the two first light beams and an interference of the two second light beams The interference measurement apparatus according to claim 7, wherein a signal obtained by receiving the other of the light beams formed by the step is estimated. The first light flux and the second light flux have different center wavelengths,
  The optical system separates the reflected light beam from the measurement surface and the reflected light beam from the reference surface by the wavelength, respectively,
  5. The light receiving unit according to claim 1, wherein the light receiving unit receives the two light fluxes obtained by the separation and outputs the first signal and the second signal. The interference measurement apparatus according to item 1. A method for determining a measurement origin for interference measurement,
A step you multiplexes the second beam having low coherence than the first light flux and the first light flux of coherent,
Wherein the first light flux which the light flux and the second light beams are combined, and divided into a portion of a part and the second light flux of the first light beam into two light beams each containing the one of the light beams obtained by the division to be incident on the measurement surface, said other light beam obtained by the division is incident on the reference surface, multiplexes the reflected light beam from the reference surface and the reflected light beam from the measuring surface And the two first light beams included in the reflected light beam from the measurement surface and the reflected light beam from the reference surface, which are combined, are caused to interfere with each other, so that the measurement surface is combined. Interfering the two second light beams respectively included in the reflected light beam from the reference beam and the reflected light beam from the reference surface;
The receiving light beams formed by the interference of two of the first light flux and outputs a first signal, a second signal by receiving the light beams formed by the interference of the two said second beam and step you output,
And determining a measurement origin based on the first signal and the second signal . The measurement origin determination method according to claim 10, wherein the first light flux and the second light flux are alternately emitted. The measurement origin determination method according to claim 11, wherein the first signal and the second signal are interpolated . Performing the other radiation of the first light flux and the second light flux and stopping the radiation while performing the radiation of one of the first light flux and the second light flux;
  As one of the first signal and the second signal, a light beam formed by interference of the two first light beams and a light beam formed by interference of the two second light beams And outputs a signal obtained by receiving both of the light beam and the other of the first signal and the second signal as a light beam formed by interference of the two first light beams and the two of the two signals. 11. The measurement origin determining method according to claim 10, wherein a signal obtained by receiving one of the light beams formed by the interference of the second light beam is output. Based on a signal obtained by receiving both and a signal obtained by receiving the one, a light beam formed by interference of the two first light beams and an interference of the two second light beams The measurement origin determination method according to claim 13, wherein a signal obtained by receiving the other of the light beams formed by the step is estimated. The first light flux and the second light flux have different center wavelengths,
  The reflected light beam from the measurement surface that has been combined and the reflected light beam from the reference surface are each separated by wavelength,
  11. The measurement origin determining method according to claim 10, wherein the two light beams obtained by the separation are respectively received and the first signal and the second signal are output.